DAKAR, Senegal (AP) -- Health workers have made dramatic progress in controlling an Ebola outbreak in West Africa in recent weeks, a doctor with the World Health Organization said Friday.

The outbreak has been blamed for the deaths of at least 168 people in Guinea and Liberia. There is no cure and no vaccine for Ebola, which causes a high fever and severe bleeding. The outbreak is unusual for West Africa as the disease is typically found in the center and east of the continent.

There are signs that the outbreak's spread is slowing, but it is not over yet, Jean-Bosco Ndihokubwayo, who is coordinating the U.N. health agency's response in Guinea, said Friday.

"The situation has improved dramatically in the last two weeks, but we're not there yet," he said.

The most recent two cases of the disease in Guinea were confirmed on Wednesday, he said, adding that the people were infected by others already known to have the disease. That's a positive sign because it means doctors are on top of the disease's contamination path, he said.

Liberia hasn't confirmed a new case since April 6, said.

Ebola can incubate for up to 21 days before an infected person shows any symptoms. Doctors like to wait 42 days -- two incubation periods -- after the last known infection before declaring an outbreak over.

So far there have been more than 240 suspected and confirmed cases of the disease, the vast majority in Guinea, said the World Health Organization.

Ndihokubwayo said the mortality rate for this outbreak thus far is close to 70 percent. He said that's within the typical range for Ebola, which can be fatal in up to 90 percent of cases.